It is known in the prior art to provide a syringe assembly with a stopper that defines and separates a first volume and a second volume within the syringe assembly. Such arrangements are used in mixing devices where two or more medicaments or other substances are mixed prior to delivery to an injection site, or in devices where two or more medicaments or other substances are delivered to an injection site separately and sequentially.
US-A-2005/0245880 (Howlett et al.) describes a multi-chamber, sequential dose dispensing syringe that has a moveable valve assembly that has a mechanical impact sensor that causes the valve to open when the valve assembly impacts (“bottoms out”) with the bottom internal end of the syringe barrel.
A two-compartment sequential dose device for sequentially delivering doses of multivitamin preparation is described in U.S. Pat. No. 3,914,419 (American Cyanamid Company). The two compartments are separated by a stopper that has a central valved passage for allowing multivitamin preparation in the upper chamber to pass out through the needle after delivery of the multivitamin preparation in the lower chamber adjacent the needle.
FR-A-2750051 (Debiotech SA) and U.S. Pat. No. 4,929,230 (Pfleger) each describe a medical syringe having a free piston slidable in the barrel of the syringe for fluidly separating two internal volumes in the syringe. The free piston maintains a sealing configuration until it bottoms out at the bottom internal end of the syringe barrel, at which point fluid from the lower volume has been delivered through the needle of the syringe under the force of an upper plunger in the barrel of the syringe. Fluid pressure in the upper volume then causes the whole free piston to deform to allow fluid from the upper volume to bypass the free piston and exit through the needle.
A similar device is described in US-A-2008/0255521 (Hisamitsu Pharmaceutical Co. Inc.) except formations at the bottom internal end of the syringe cause the free piston to deform allowing fluid in the upper volume to bypass the free piston and exit the syringe through the needle.
Another syringe for sequentially administering different fluids is described in US-A-2004/0171984 (Greenfield) which also has a floating piston which acts to selectively separate two fluid volumes in the syringe. In one described embodiment, the floating piston is made of a compressible body that has a central valve that opens upon axial compression of the body.
U.S. Pat. No. 5,713,857 (Becton Dickinson France, S.A.) describes a stopper for use in a sequential delivery device. The stopper has a collapsible portion down one side that collapses when a predetermined fluid pressure is exceeded such that an axial channel is opened up along the side of the stopper. Thus, in a collapsed configuration, the stopper no longer forms a complete circumferential seal with the inner surface of the syringe barrel to allow the passage of fluid.
An automatic injection device for mixing a dry medicament component and a fluid (such as a diluent) and subsequently delivering the mixture/solution is described in US-A-2002/042592 (Wilmot, John G. et al.). A floating stopper initially separates the dry component from the wet component and is moveable to a position where a fluid passageway is opened which fluidly connects the volumes containing the wet and dry components. The fluid passageway is described as recesses (acting as bypass channels) in the inner surface of the syringe barrel. In an alternative described embodiment, the inner surface of the syringe barrel comprises ribs that distort the stopper when it reaches a particular axial position within the barrel to allow fluid to bypass the stopper and mix with the dry component.
A further two-compartment syringe is described in EP-A-0112574 (Meditec S.A.) which has a floating stopper having a central valve assembly for selectively allowing fluid communication between the two volumes separated by the stopper. The central valve assembly consists of a blocking component moveable relative to the remainder of the stopper between a blocking position where the central valve assembly is closed and an open position where the central valve assembly is open and fluidly connects the two compartments. The blocking component is biased by a spring to the blocking position so that a force (such as fluid pressure) is required to move the blocking component to the open position.
An automatic injector device is described in WO-A-9409839 which has a plunger rod disposed in a syringe barrel with a flexible stopper at the end of the plunger rod. Initially, the flexible stopper separates a dry medicament component from a fluid in a compartment rear of the dry compartment. The plunger rod and flexible stopper are moved rearwardly into the fluid compartment to initiate mixing as the flexible element flexes during movement through the fluid allowing fluid to bypass the flexible element and mix with the dry component. To actuate delivery of the mixed medicament, a rigid stopper is moved forward through the barrel of the syringe to expel mixed medicament from the syringe through the needle.
It is an object of the present invention to provide an improved or alternative syringe assembly that permits the selective separation of volume spaces therein.